The present invention is related to handbrakes for railway cars and in particular to a handbrake tensioning member that compensates for slack in the handbrake system, in order to prevent undesired loss of the handbrake application force.
Traditional railway car handbrake systems employ a car mounted handwheel device to which one end of a handbrake chain is connected. The other end of the handbrake chain is connected to a handbrake lever via which the car brakes are applied in a well-known manner.
Railway car handbrakes are employed to hold a car or cut of cars on the siding when removed from a train, since the automatic air brake becomes ineffective over a period of time due to the car air pressure gradually leaking off. There have been incidences of such parked cars running away, even though their handbrakes were properly applied. Such incidences have occurred on cars with truck mounted brakes and are attributed to relative movement between the car body and truck, which results in handbrake chain slack and a loss of chain tension, with consequent loss of handbrake force. While a certain minimal amount of relative movement between the car body and truck is normal, it can be exacerbated by wear of the interface components via which the car body is mounted on the truck, as for example the car center plate, the center plate bowl on the bolster and/or the center plate wear liner. While handbrake forces are normally insufficient to effect any relative movement between the car body and truck under static conditions of friction therebetween, as normally exists at the time a handbrake application is made, tests have shown that vibration forces in a railway environment are strong enough to "break" away this static friction, so that the handbrake force becomes effective to gradually shift the car body relative to the truck and accordingly reduce the handbrake chain tension sufficiently to release or significantly reduce the applied handbrake force.